U.S. patent application number 13/084126 was filed with the patent office on 2011-09-08 for rubber outer covers for golf balls based on ethylene-propylene diene copolymers.
Invention is credited to Mark L. Binette, Dennis Britton, David A. Bulpett, Brian Comeau, William E. Morgan, Michael J. Sullivan.
Application Number | 20110218054 13/084126 |
Document ID | / |
Family ID | 44531807 |
Filed Date | 2011-09-08 |
United States Patent
Application |
20110218054 |
Kind Code |
A1 |
Sullivan; Michael J. ; et
al. |
September 8, 2011 |
RUBBER OUTER COVERS FOR GOLF BALLS BASED ON ETHYLENE-PROPYLENE
DIENE COPOLYMERS
Abstract
A multi-piece golf ball comprising at least one component made
of an ethylene-propylene diene copolymer (EPDM) rubber is provided.
The multi-piece golf ball includes a cover, preferably a dual-cover
having inner and outer cover layers. The outer cover is preferably
made of the EPDM rubber material. The golf ball further includes an
inner core, preferably a dual-core containing a center and
surrounding outer core layer. The center may be made of a
polybutadiene rubber composition and the outer core layer may be
made of an EPDM rubber composition. The resulting golf ball has
high resiliency, a soft feel, and good weatherability.
Inventors: |
Sullivan; Michael J.;
(Barrington, RI) ; Bulpett; David A.; (Boston,
MA) ; Comeau; Brian; (Berkley, MA) ; Binette;
Mark L.; (Mattapoisett, MA) ; Morgan; William E.;
(Barrington, RI) ; Britton; Dennis; (North
Dartmouth, MA) |
Family ID: |
44531807 |
Appl. No.: |
13/084126 |
Filed: |
April 11, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12717543 |
Mar 4, 2010 |
|
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13084126 |
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Current U.S.
Class: |
473/373 ;
473/377; 473/378; 473/385 |
Current CPC
Class: |
A63B 37/12 20130101;
A63B 37/06 20130101; A63B 37/02 20130101 |
Class at
Publication: |
473/373 ;
473/378; 473/385; 473/377 |
International
Class: |
A63B 37/12 20060101
A63B037/12; A63B 37/02 20060101 A63B037/02; A63B 37/06 20060101
A63B037/06 |
Claims
1. A multi-layered golf ball, comprising: a solid core of at least
one layer; and a cover disposed about the core, the cover
comprising an inner layer and outer layer, the outer layer being
formed from a first rubber composition comprising
ethylene-propylene-diene copolymer rubber; a polymerization
initiator; and a reactive cross-linking co-agent, wherein the
rubber composition is subjected to a cross-linking reaction.
2. The golf ball of claim 1, wherein the outer layer is formed from
a thermoset liquid rubber composition comprising liquid
ethylene-propylene-diene copolymer rubber.
3. The golf ball of claim 1, wherein the polymerization initiator
is a peroxide.
4. The golf ball of claim 1, wherein the cross-linking co-agent is
a metal salt of an .alpha.,.beta. unsaturated carboxylic acid.
5. The golf ball of claim 1, wherein the rubber composition further
comprises a filler selected from the group consisting of polymeric,
metal, and mineral fillers and mixtures thereof.
6. The golf ball of claim 1, wherein the core is single-layered,
the core being formed from a second rubber composition comprising
polybutadiene rubber.
7. The golf ball of claim 1, wherein the core is dual-layered, the
core comprising an inner core and outer core layer, the inner core
being formed from a second rubber composition comprising
polybutadiene rubber, and the outer core layer being formed from a
third rubber composition comprising ethylene-propylene-diene
copolymer rubber.
8. The golf ball of claim 6, wherein the core has a diameter of
about 1.45 to about 1.59 inches.
9. The golf ball of claim 7, wherein the inner core has a diameter
of about 0.40 to about 1.55 inches.
10. The golf ball of claim 7, wherein the outer core has a
thickness of about 0.020 to about 0.150 inches.
11. The golf ball of claim 7, wherein the dual core has an overall
diameter of about 1.51 to about 1.62 inches
12. The golf ball of claim 1, wherein the first rubber composition
further comprises an elastomer selected from the group consisting
of polybutadiene, ethylene-propylene rubber, polyisoprene,
styrene-butadiene rubber, polyalkenamers, butyl rubber, halobutyl
rubber, polystyrene elastomers, polyethylene elastomers,
polyurethane elastomers, polyurea elastomers, metallocene-catalyzed
elastomers and plastomers, copolymers of isobutylene and
p-alkylstyrene, halogenated copolymers of isobutylene and
p-alkylstyrene, copolymers of butadiene with acrylonitrile,
polychloroprene, alkyl acrylate rubber, chlorinated isoprene
rubber, acrylonitrile chlorinated isoprene rubber, and mixtures
thereof.
13. The golf ball of claim 1, wherein the inner cover layer is
formed from an ionomeric resin comprising a copolymer of
.alpha.-olefin, C.sub.3 to C.sub.8 .alpha.,.beta.-ethylenically
unsaturated mono- or dicarboxylic acid, and optional softening
monomer.
14. The golf ball of claim 13, wherein the ionomeric resin contains
greater than 16 weight percent acid groups.
15. The golf ball of claim 13, wherein the ionomeric resin contains
less than 16 weight percent acid groups.
16. The golf ball of claim 1, wherein the inner cover layer has a
material hardness of 60 Shore D or greater.
17. The golf ball of claim 1, wherein the outer cover layer has a
thickness in the range of about 0.010 to about 0.080 inches.
18. The golf ball of claim 1, wherein the outer cover layer has a
material hardness of 60 Shore D or less.
19. The golf ball of claim 1, wherein the inner cover is formed
from a second rubber composition comprising EPDM copolymer rubber,
a polymerization initiator, and a reactive cross-linking agent.
20. The golf ball of claim 27, wherein the inner cover has a
hardness of 55 Shore D or greater and the outer cover has a
hardness of 55 Shore D or less.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation-in-part of co-pending,
co-assigned U.S. patent application Ser. No. 12/717,543 having a
filing date of Mar. 4, 2010, the entire disclosure of which is
hereby incorporated by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention generally relates to multi-piece golf
balls and more particularly to golf balls having at least one
component made of a composition comprising an ethylene-propylene
diene copolymer (EPDM) rubber. The multi-piece golf ball includes
an inner core, preferably a dual-core containing a center and
surrounding outer core layer. The golf ball further includes a
cover, preferably a dual-cover having inner and outer cover layers.
The outer cover preferably is made of the EPDM rubber. The
resulting golf ball has high resiliency, a soft feel, and good
weather-resistance.
[0004] 2. Brief Review of the Related Art
[0005] Multi-piece solid golf balls having a core and surrounding
cover are generally known in the industry. Basically, a two-piece
solid golf ball includes a solid inner core protected by an outer
cover. The inner core is made commonly of a rubber material such as
natural and synthetic rubbers: styrene butadiene, polybutadiene,
poly(cis-isoprene), or poly(trans-isoprene). The outer cover is
made commonly of a thermoplastic such as ionomer resins,
polyamides, and polyesters; and thermoplastic and thermoset
polyurethane and polyurea elastomers. As new materials and
manufacturing processes have become more economically feasible,
three-piece, four-piece, and five-piece solid golf balls have been
introduced. Both professional and amateur golfers enjoy these
multi-piece golf balls because of their properties and playing
performance. Different materials can be used to impart specific
properties and playing features to the ball.
[0006] Multi-layered covers are used normally in constructing these
multi-piece balls. For example, the ball may include an inner cover
layer made of an ethylene-based acid copolymer ionomer resin that
helps impart hardness to the ball. These acid copolymer ionomers
contain inter-chain ionic bonding and are generally made of an
.alpha.-olefin such as ethylene and a vinyl comonomer having an
acid group such as methacrylic, acrylic acid, or maleic acid. Metal
ions such as sodium, lithium, zinc, and magnesium are used to
neutralize the acid groups in the copolymer. Commercially available
ethylene-based ionomer resins are available in various grades and
identified based on type of base resin, molecular weight, and type
of metal ion, amount of acid, degree of neutralization, additives,
and other properties. The outer cover layer, which is disposed
about the inner cover layer, may be made from a variety of
materials including ionomers, polyamides, polyesters, and
thermoplastic and thermoset polyurethane and polyureas. In recent
years, golf balls having thin polyurethane covers have become more
popular, because such covers tend to provide the ball with a "soft
feel." In general, these balls provide the player with a more
natural feel and sensation when he/she strikes the ball with the
club face as opposed to balls having a more plastic and "hard
feel."
[0007] Various cover materials are known in the industry. For
example, Nesbitt, U.S. Pat. No. 6,303,704 discloses golf balls
having covers made of non-ionomeric resins that have been subjected
to cross-linking by peroxide cross-linking agents such as dicumyl
peroxide or by irradiation such as gamma rays/electron beams.
Numerous resin materials are listed including ethylene-ethyl
acrylate, ethylene-methyl acrylate, ethylene-vinyl acetate, low
density polyethylene, linear low density polyethylene, metallocene
catalyzed polyolefins, polyamides, non-ionomeric acid copolymers,
ethylene propylene elastomers such as EPR and EPDM, and
syndiotactic resins such as syndiotactic 1,2-polybutadiene alone or
in combination with other dienes. In one embodiment, a cover
composition made from 100 parts ethylene-propylene-diene monomer
and additives was cross-linked. The resulting composition was
molded over a solid core to form a two-piece ball that was tested
for scuff and cut-resistance.
[0008] Sullivan and Kaltenbacher, U.S. Pat. No. 5,857,926 discloses
a cover layer formed from a composition comprising a blend of: 1)
ionomeric copolymer; 2) ethylene-propylene-diene monomer; and 3) a
copolymer formed from an .alpha.-olefin such as ethylene, acrylate
ester such as methylacrylate, and acid such as methacrylic acid.
The cover composition may be molded over a golf ball core (solid or
wound) by injection molding or compression molding. Cores having
one, two, or more layers can be used. According to the '926 patent,
the resulting ball has a high coefficient of restitution, soft
cover, and excellent cut-resistance.
[0009] The industry continues looking for new cover materials for
golf balls. It would be desirable to have a cover material that
helps provides the ball with high resiliency. This would help the
ball travel longer distances. At the same time, the cover material
should provide the ball with a nice feel and playability. The cover
material should not be excessively hard. Moreover, it would be
desirable to have a cover material with high weather-resistance so
the ball can resist cracking and thermal aging. The present
invention provides golf balls having covers with such properties as
well as other advantageous characteristics and features.
SUMMARY OF THE INVENTION
[0010] The present invention provides a multi-piece golf ball
comprising at least one component made of an
ethylene-propylene-diene copolymer (EPDM) rubber composition. In
one embodiment, the ball contains a solid core of at least one
layer and a cover enclosing the core. Preferably, the cover
includes inner and outer cover layers, wherein the inner cover
layer is formed of an ethylene-based acid copolymer ionomer resin
and the outer cover is formed of a rubber composition comprising an
EPDM rubber. The EPDM composition further comprises a
polymerization initiator and reactive cross-linking co-agent and it
is subjected to a cross-linking reaction.
[0011] In the EPDM rubber compositions, the polymerization
initiator is preferably a peroxide and the cross-linking co-agent
is preferably a metal salt of an .alpha.,.beta. unsaturated
carboxylic acid. Preferably, the EPDM rubber composition further
comprises filler selected from the group consisting of polymeric,
metal, and mineral fillers and mixtures thereof. In a dual-core
construction, the inner core normally has a diameter of about 0.40
to about 1.55 inches, and the outer core normally has a thickness
of about 0.020 to about 0.150 inches. The core normally has an
overall diameter of about 1.45 to about 1.59 inches.
[0012] In the dual-covers, the inner cover layer may have a surface
hardness of 60 Shore D or greater, and the outer cover layer may
have a surface hardness of 20 to 70 Shore D, wherein the hardness
of the inner cover layer is greater than the hardness of the outer
cover. Preferably, the inner cover layer is formed from an
ionomeric resin, comprising a copolymer of .alpha.-olefin, C.sub.3
to C.sub.8 .alpha.,.beta.-ethylenically unsaturated mono- or
dicarboxylic acid, and optional softening monomer. The ionomeric
resin may be an E/X/Y copolymer, wherein E is ethylene; X is a
C.sub.3 to C.sub.8 .alpha.,.beta.-ethylenically unsaturated mono-
or dicarboxylic acid; and Y is a softening monomer. For example,
copolymers selected from the group consisting of:
ethylene/(meth)acrylic acid/n-butyl acrylate;
ethylene/(meth)acrylic acid/ethyl acrylate; ethylene/(meth)acrylic
acid/methyl acrylate; ethylene/(meth)acrylic acid/n-butyl acrylate;
and ethylene/(meth)acrylic acid/isobutyl acrylate copolymers may be
used. High acid ionomers containing greater than 16 weight percent
acid groups may be used as well as low acid ionomers. The acid
groups may be neutralized greater than 70% and preferably greater
than 90%.
[0013] In another embodiment, the outer cover is formed from a
first rubber composition comprising EPDM copolymer rubber so that
the outer cover has a hardness of 55 Shore D or less. Meanwhile,
the inner cover is formed from a second rubber composition
comprising EPDM copolymer rubber so that the inner cover has a
hardness of 55 Shore D or greater.
[0014] The EPDM rubber composition may further contain an elastomer
selected from the group consisting of polybutadiene,
ethylene-propylene rubber, polyisoprene, styrene-butadiene rubber,
polyalkenamers, butyl rubber, halobutyl rubber, polystyrene
elastomers, polyethylene elastomers, polyurethane elastomers,
polyurea elastomers, metallocene-catalyzed elastomers and
plastomers, copolymers of isobutylene and p-alkylstyrene,
halogenated copolymers of isobutylene and p-alkylstyrene,
copolymers of butadiene with acrylonitrile, polychloroprene, alkyl
acrylate rubber, chlorinated isoprene rubber, acrylonitrile
chlorinated isoprene rubber, and mixtures thereof.
[0015] In one embodiment, the golf ball contains a dual-core
comprising an inner core (center) and surrounding outer core layer.
The inner core has a geometric center and outer surface, while the
outer core layer has an inner surface and outer surface. The
material hardness of the inner core is preferably greater than the
outer surface hardness of the outer core layer. Preferably, an EPDM
rubber composition is used to form the outer core layer and a
polybutadiene rubber is used to form the inner core. In one
version, the center hardness of the inner core is in the range of
about 75 Shore C to about 90 Shore C units, and the outer surface
of the outer core is preferably in the range of about 50 to about
70 Shore C. Preferably, the center hardness of the inner core is in
the range of about 52 to about 98 Shore C units and the surface
hardness of the outer core is in the range of about 50 to 96 Shore
C units. More preferably, the center hardness is about 80 Shore C
or greater, and the surface hardness of the outer core is about 80
Shore C or less.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] The novel features that are characteristic of the present
invention are set forth in the appended claims. However, the
preferred embodiments of the invention, together with further
objects and attendant advantages, are best understood by reference
to the following detailed description in connection with the
accompanying drawings in which:
[0017] FIG. 1 is a cross-sectional view of a three-piece golf ball
having an inner core and a dual-cover comprising inner and outer
cover layers, the outer cover layer being formed of an EPDM rubber
composition;
[0018] FIG. 2 is a cross-sectional view of a four-piece golf ball
having a dual-core comprising an inner core and outer core layer
and dual-cover comprising inner and outer cover layers, wherein the
outer cover layer is made of an EPDM rubber composition;
[0019] FIG. 3 is a cross-sectional view of a five-piece golf ball
having a three layered-core comprising an inner core, intermediate
core layer, and outer core and a cover comprising inner and outer
cover layers, wherein the outer cover layer is made of made of an
EPDM rubber composition; and
[0020] FIG. 4 is a front view of a golf ball having a dimpled cover
made in accordance with the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0021] The present invention relates generally to golf balls
containing at least one component made from a composition
comprising ethylene-propylene-diene copolymer (EPDM) rubber. The
golf ball may contain a single core or dual-core comprising an
inner core (center) and surrounding outer core layer. Preferably,
the ball includes a dual-cover comprising inner cover and outer
cover layers, the inner cover layer being made of an ethylene-based
acid copolymer ionomer and the outer cover layer being made of a
rubber composition comprising EPDM.
[0022] Golf balls having various constructions may be made in
accordance with this invention. For example, golf balls having
three-piece, four-piece, and five-piece constructions with dual or
three-layered cores and cover materials may be made The term,
"layer" as used herein means generally any spherical portion of the
golf ball. More particularly, in one version, a three-piece golf
ball comprising a "dual-core" and cover is made. In another
version, a four-piece golf ball comprising a dual-core and
"dual-cover" is made. The dual-core includes an inner core (center)
and surrounding outer core layer. The dual-cover includes inner
cover and outer cover layers. In yet another construction, a
five-piece golf ball having a dual-core, intermediate layer, and
dual-cover is made. As used herein, the term, "intermediate layer"
means a layer of the ball disposed between the core and cover. The
intermediate layer may be considered an outer core layer, or inner
cover layer, or any other layer disposed between the inner core and
outer cover of the ball. The intermediate layer also may be
referred to as a casing or mantle layer. In accordance with the
present invention, at least one of the core, intermediate, and
cover layers of the golf ball is formed from the rubber composition
of this invention. The diameter and thickness of the different
layers along with properties such as hardness and compression may
vary depending upon the construction and desired playing
performance properties of the golf ball.
[0023] Ethylene-Propylene-Diene Copolymer Rubber
[0024] Preferably, the outer cover layer is formed of a first
rubber composition comprising ethylene-propylene-diene (EPDM)
copolymer rubber. In one version, the catalyzed EPDM rubber
comprises from about 70% to about 90% by weight of ethylene and
about 1 to about 5% ethylidene-2-norborene.
[0025] The EPDM rubber may have a relatively high or low Mooney
viscosity. A "Mooney unit" is an arbitrary unit used to measure the
viscosity of raw or non-vulcanized rubber. In the present
invention, the Mooney viscosity is measured in accordance with
"Standard Test Methods for Rubber-Viscosity, Stress Relaxation, and
Pre-Vulcanization Characteristics (Mooney Viscometer)" of ASTM
D1646-07. In general, EPDM rubbers of higher molecular weight and
higher Mooney viscosity have better resiliency than EPDM rubbers of
lower molecular weight and lower Mooney viscosity. However, as the
Mooney viscosity increases, the milling and processing of the EPDM
rubber generally becomes more difficult. In general, the lower
limit of Mooney viscosity may be 30 or 35 or 40 or 45 or 50 or 55
or 60 or 70 or 75 and the upper limit may be 80 or 85 or 90 or 95
or 100 or 105 or 110 or 115 or 120 or 125 or 130. Blends of high
and low Mooney viscosity EPDM copolymer rubbers may be
prepared.
[0026] Examples of commercially available EPDM rubbers that can be
used in accordance with this invention include, but are not limited
to, NORDEL IP, available from Dow Chemical (Midland, Mich.); BUNA
EP, available from Lanxess Corp. (Pittsburgh, Pa.); VISTALON,
available from ExxonMobil (Irving, Tex.); and Royalene and
RoyalEdge, available from Lion CoPolymer (Baton Rouge, La.). Maleic
anhydride-modified EPDM such as RoyalFlex and silicone-modified
EPDM such as Royaltherm, available from Lion Copolymer, may be
used. In other instances, as discussed further below, a liquid EPDM
rubber such as TRILENE, available from Lion Copolymer, may be
used.
[0027] The EPDM rubber material (base rubber) may be blended with
other elastomers in accordance with this invention. Other
elastomers include, but are not limited to, polybutadiene,
polyisoprene, ethylene propylene rubber ("EPR"), styrene-butadiene
rubber, styrenic block copolymer rubbers (such as "SI", "SIS",
"SB", "SBS", "SIBS", and the like, where "S" is styrene, "I" is
isobutylene, and "B" is butadiene), polyalkenamers such as, for
example, polyoctenamer, butyl rubber, halobutyl rubber, polystyrene
elastomers, polyethylene elastomers, polyurethane elastomers,
polyurea elastomers, metallocene-catalyzed elastomers and
plastomers, copolymers of isobutylene and p-alkylstyrene,
halogenated copolymers of isobutylene and p-alkylstyrene,
copolymers of butadiene with acrylonitrile, polychloroprene, alkyl
acrylate rubber, chlorinated isoprene rubber, acrylonitrile
chlorinated isoprene rubber, and combinations of two or more
thereof.
[0028] The EPDM rubber is used in an amount of at least about 50%
by weight based on total weight of composition and is generally
present in an amount of about 50% to about 100%, or an amount
within a range having a lower limit of 50% or 60% or 70% and an
upper limit of 80% or 90% or 100%. Preferably, the concentration of
EPDM rubber is about 50 to about 75 weight percent and more
preferably about 55 to about 70 weight percent.
[0029] In one preferred embodiment, a liquid EPDM rubber is used.
The liquid rubber composition may be a relatively low molecular
weight pure liquid polymer such as TRILENE liquid EPDM rubber,
available from Lion Copolymer. Or, the liquid rubber may contain be
a latex material containing an emulsion of rubber globules in
water. In one version, the liquid rubber is a latex material
containing about 30% to about 70% solids. As described in
co-pending, co-assigned U.S. patent application Ser. No.
12/717,543, the disclosure of which is incorporated by reference,
the liquid rubber composition may be a latex material that, when in
a solid state, can be extended under ambient conditions at least
twice its resting length, and upon stress release can return to
within 15% of its original length. The latex material may form a
heavy latex film with about 30% to about 70% solids and applied
using submersion times of about 10 seconds to about 60 seconds. The
preferred method of application of the latex is submersion of the
core in a bath; however, other methods can be used. It is useful in
this invention that the liquid dry to a reasonably tack-free film
or a film which can be rendered tack-free by exposure to heat or
radiation. However, a heavy latex film can be formed with less than
30% solids, if the submersion time is increased accordingly or with
more than 70% solids if the submersion time is decreased
accordingly. The preferred heavy latex material has about 52%
solids and is applied using a submersion time of about 30 seconds
The liquid rubber composition typically has a viscosity of about
10,000 cp or less, more preferably from about 1,000 cp to 10,000
cp, or, optionally, about 1,000 cp or less.
[0030] In accordance with the present invention, golf balls
containing dual-covers having an outer cover layer formed from a
rubber composition comprising EPDM rubber have advantageous
properties. Particularly, the EPDM rubber composition can be used
to make an outer cover layer that provides the golf ball with good
rebounding properties (distance) without sacrificing a nice feel to
the ball. The resulting ball has a relatively high coefficient of
restitution ("COR") allowing it to reach high velocity when struck
by a golf club. Thus, the ball tends to travel a greater distance
which is particularly important for driver shots off the tee. At
the same time, the EPDM rubber composition is not excessively hard
and it helps provide the ball with a soft and comfortable feel. The
golf player experiences a better sense of control and natural
feeling when striking the ball. Furthermore, the softer cover
allows players to place a spin on the ball and better control its
flight pattern. The ball has better playability. This is
particularly important for approach shots near the green. Moreover,
the EPDM rubber composition used to form the cover helps impart
good weather-resistance to the ball. Thus, the ball should have
good crack resistance and the effects of sunlight, and freezing and
heated temperatures should be less harmful.
[0031] As discussed further below, the base (and dominant)
component in the EPDM rubber composition is the EPDM copolymer
rubber. The composition preferably further contains a cross-linking
initiator agent such as peroxide and a reactive cross-linking
co-agent such as zinc diacrylate, but these ingredients are added
in lesser amounts. There is minimal amount of cross-linking in the
EPDM rubber composition and this helps to impart a soft feel to the
ball.
[0032] Polybutadiene Rubber
[0033] Preferably, the inner core of the golf ball is formed of a
second rubber composition comprising a polybutadiene rubber
material. In one embodiment, the ball contains a single core formed
of the polybutadiene rubber composition. In a second embodiment,
the ball contains a dual-core comprising an inner core (center) and
surrounding outer core layer. In yet another version, the golf ball
contains a multi-layered core comprising an inner core,
intermediate core layer, and outer core layer. Preferably, the
inner core is made of a rubber composition comprising polybutadiene
and the outer core layer is made of a rubber composition comprising
EPDM.
[0034] In general, polybutadiene is a homopolymer of 1,3-butadiene.
The double bonds in the 1,3-butadiene monomer are attacked by
catalysts to grow the polymer chain and form a polybutadiene
polymer having a desired molecular weight. Any suitable catalyst
may be used to synthesize the polybutadiene rubber depending upon
the desired properties. Normally, a transition metal complex (for
example, neodymium, nickel, or cobalt) or an alkyl metal such as
alkyllithium is used as a catalyst. Other catalysts include, but
are not limited to, aluminum, boron, lithium, titanium, and
combinations thereof. The catalysts produce polybutadiene rubbers
having different chemical structures. In a cis-bond configuration,
the main internal polymer chain of the polybutadiene appears on the
same side of the carbon-carbon double bond contained in the
polybutadiene. In a trans-bond configuration, the main internal
polymer chain is on opposite sides of the internal carbon-carbon
double bond in the polybutadiene. The polybutadiene rubber can have
various combinations of cis- and trans-bond structures. A preferred
polybutadiene rubber has a 1,4 cis-bond content of at least 40%,
preferably greater than 80%, and more preferably greater than 90%.
In general, polybutadiene rubbers having a high 1,4 cis-bond
content have high tensile strength. The polybutadiene rubber may
have a relatively high or low Mooney viscosity.
[0035] Examples of commercially available polybutadiene rubbers
that can be used in accordance with this invention, include, but
are not limited to, BR 01 and BR 1220, available from BST
Elastomers of Bangkok, Thailand; SE BR 1220LA and SE BR1203,
available from DOW Chemical Co of Midland, Mich.; BUDENE 1207,
1207s, 1208, and 1280 available from Goodyear, Inc of Akron, Ohio;
BR 01, 51 and 730, available from Japan Synthetic Rubber (JSR) of
Tokyo, Japan; BUNA CB 21, CB 22, CB 23, CB 24, CB 25, CB 29 MES, CB
60, CB Nd 60, CB 55 NF, CB 70 B, CB KA 8967, and CB 1221, available
from Lanxess Corp. of Pittsburgh. Pa.; BR1208, available from LG
Chemical of Seoul, South Korea; UBEPOL BR130B, BR150, BR150B,
BR150L, BR230, BR360L, BR710, and VCR617, available from UBE
Industries, Ltd. of Tokyo, Japan; EUROPRENE NEOCIS BR 60, INTENE 60
AF and P30AF, and EUROPRENE BR HV80, available from Polimeri Europa
of Rome, Italy; AFDENE 50 and NEODENE BR40, BR45, BR50 and BR60,
available from Karbochem (PTY) Ltd. of Bruma, South Africa; KBR 01,
NdBr 40, NdBR-45, NdBr 60, KBR 710S, KBR 710H, and KBR 750,
available from Kumho Petrochemical Co., Ltd. Of Seoul, South Korea;
DIENE 55NF, 70AC, and 320 AC, available from Firestone Polymers of
Akron, Ohio; and PBR-Nd Group II and Group III, available from
Nizhnekamskneftekhim, Inc. of Nizhnekamsk, Tartarstan Republic.
[0036] To form the core, the polybutadiene rubber is used in an
amount of at least about 5% by weight based on total weight of
composition and is generally present in an amount of about 5% to
about 100%, or an amount within a range having a lower limit of 5%
or 10% or 20% or 30% or 40% or 50% and an upper limit of 55% or 60%
or 70% or 80% or 90% or 95% or 100%. Preferably, the concentration
of polybutadiene rubber is about 45 to about 95 weight percent.
[0037] Curing of Rubber Compositions
[0038] The rubber compositions of this invention may be cured,
either pre-blending or post-blending, using conventional curing
processes. Suitable curing processes include, for example,
peroxide-curing, sulfur-curing, high-energy radiation, and
combinations thereof. Preferably, the rubber composition contains a
free-radical initiator selected from organic peroxides, high energy
radiation sources capable of generating free-radicals, and
combinations thereof. In one preferred version, the rubber
composition is peroxide-cured. Suitable organic peroxides include,
but are not limited to, dicumyl peroxide;
n-butyl-4,4-di(t-butylperoxy) valerate;
1,1-di(t-butylperoxy)3,3,5-trimethylcyclohexane;
2,5-dimethyl-2,5-di(t-butylperoxy) hexane; di-t-butyl peroxide;
di-t-amyl peroxide; t-butyl peroxide; t-butyl cumyl peroxide;
2,5-dimethyl-2,5-di(t-butylperoxy)hexyne-3;
di(2-t-butyl-peroxyisopropyl)benzene; dilauroyl peroxide; dibenzoyl
peroxide; t-butyl hydroperoxide; and combinations thereof. In a
particular embodiment, the free radical initiator is dicumyl
peroxide, including, but not limited to Perkadox.RTM. BC,
commercially available from Akzo Nobel. Peroxide free-radical
initiators are generally present in the rubber composition in an
amount of at least 0.05 parts by weight per 100 parts of the total
rubber, or an amount within the range having a lower limit of 0.05
parts or 0.1 parts or 1 part or 1.25 parts or 1.5 parts or 2.5
parts or 5 parts by weight per 100 parts of the total rubbers, and
an upper limit of 2.5 parts or 3 parts or 5 parts or 6 parts or 10
parts or 15 parts by weight per 100 parts of the total rubber.
Concentrations are in parts per hundred (phr) unless otherwise
indicated. As used herein, the term, "parts per hundred," also
known as "phr" or "pph" is defined as the number of parts by weight
of a particular component present in a mixture, relative to 100
parts by weight of the polymer component. Mathematically, this can
be expressed as the weight of an ingredient divided by the total
weight of the polymer, multiplied by a factor of 100.
[0039] The rubber compositions may further include a reactive
cross-linking co-agent. Suitable co-agents include, but are not
limited to, metal salts of unsaturated carboxylic acids having from
3 to 8 carbon atoms; unsaturated vinyl compounds and polyfunctional
monomers (e.g., trimethylolpropane trimethacrylate); phenylene
bismaleimide; and combinations thereof. Particular examples of
suitable metal salts include, but are not limited to, one or more
metal salts of acrylates, diacrylates, methacrylates, and
dimethacrylates, wherein the metal is selected from magnesium,
calcium, zinc, aluminum, lithium, and nickel. In a particular
embodiment, the co-agent is selected from zinc salts of acrylates,
diacrylates, methacrylates, and dimethacrylates. In another
particular embodiment, the agent is zinc diacrylate (ZDA). When the
co-agent is zinc diacrylate and/or zinc dimethacrylate, the
co-agent is typically included in the rubber composition in an
amount within the range having a lower limit of 1 or 5 or 10 or 15
or 19 or 20 parts by weight per 100 parts of the total rubber, and
an upper limit of 24 or 25 or 30 or 35 or 40 or 45 or 50 or 60
parts by weight per 100 parts of the base rubber.
[0040] Radical scavengers such as a halogenated organosulfur,
organic disulfide, or inorganic disulfide compounds may be added to
the rubber composition. These compounds also may function as "soft
and fast agents." As used herein, "soft and fast agent" means any
compound or a blend thereof that is capable of making a core: 1)
softer (having a lower compression) at a constant "coefficient of
restitution" (COR); and/or 2) faster (having a higher COR at equal
compression), when compared to a core equivalently prepared without
a soft and fast agent. Preferred halogenated organosulfur compounds
include, but are not limited to, pentachlorothiophenol (PCTP) and
salts of PCTP such as zinc pentachlorothiophenol (ZnPCTP). Using
PCTP and ZnPCTP in golf ball inner cores helps produce softer and
faster inner cores. The PCTP and ZnPCTP compounds help increase the
resiliency and the coefficient of restitution of the core. In a
particular embodiment, the soft and fast agent is selected from
ZnPCTP, PCTP, ditolyl disulfide, diphenyl disulfide, dixylyl
disulfide, 2-nitroresorcinol, and combinations thereof.
[0041] The rubber compositions of the present invention also may
include "fillers," which are added to adjust the density and/or
specific gravity of the material. Suitable fillers include, but are
not limited to, polymeric or mineral fillers, metal fillers, metal
alloy fillers, metal oxide fillers and carbonaceous fillers.
Fillers can be in the form of flakes, fibers, fibrils, or powders.
Regrind, which is ground, recycled core material (for example,
ground to about 30 mesh particle size), can also be used. The
amount and type of fillers utilized are governed by the amount and
weight of other ingredients in the golf ball, since a maximum golf
ball weight of 45.93 g (1.62 ounces) has been established by the
United States Golf Association (USGA).
[0042] As discussed above, the golf ball preferably contains a
dual-core comprising an inner core (center) and surrounding outer
core layer. In one embodiment, the specific gravity of the center
is preferably less than or equal to or substantially the same as
the specific gravity of the outer core layer. For purposes of the
present invention, specific gravities are substantially the same if
they are the same or within 0.1 g/cc of each other. Preferably, the
center has a specific gravity within a range having a lower limit
of 0.50 or 0.90 or 1.05 or 1.13 g/cc and an upper limit of 1.15 or
1.18 or 1.20 g/cc. The outer core layer preferably has a specific
gravity of 1.00 g/cc or greater, or 1.05 g/cc or greater, or 1.10
g/cc or greater. In one embodiment, the outer core has a specific
gravity in the range of about 1.00 to about 1.18 g/cc. As discussed
further below, if an intermediate core layer is present, it
preferably has a specific gravity of 1.00 g/cc or greater, or 1.05
g/cc or greater, or 1.10 g/cc or greater. In a particularly
preferred embodiment, the specific gravities of the center and
outer core layer are substantially the same. In another
particularly preferred embodiment, the specific gravities of the
intermediate layer and outer core layer are substantially the
same.
[0043] Suitable polymeric or mineral fillers include, for example,
precipitated hydrated silica, clay, talc, asbestos, glass fibers,
aramid fibers, mica, calcium metasilicate, barium sulfate, zinc
sulfide, lithopone, silicates, silicon carbide, diatomaceous earth,
polyvinyl chloride, carbonates such as calcium carbonate and
magnesium carbonate. Suitable metal fillers include titanium,
tungsten, aluminum, bismuth, nickel, molybdenum, iron, lead,
copper, boron, cobalt, beryllium, zinc, and tin. Suitable metal
alloys include steel, brass, bronze, boron carbide whiskers, and
tungsten carbide whiskers. Suitable metal oxide fillers include
zinc oxide, iron oxide, aluminum oxide, titanium oxide, magnesium
oxide, and zirconium oxide. Suitable particulate carbonaceous
fillers include graphite, carbon black, cotton flock, natural
bitumen, cellulose flock, and leather fiber. Micro balloon fillers
such as glass and ceramic, and fly ash fillers can also be
used.
[0044] In addition, the rubber compositions may include
antioxidants to prevent the breakdown of the elastomers. Also,
processing aids such as high molecular weight organic acids and
salts thereof, may be added to the composition. Suitable organic
acids are aliphatic organic acids, aromatic organic acids,
saturated mono-functional organic acids, unsaturated monofunctional
organic acids, multi-unsaturated mono-functional organic acids, and
dimerized derivatives thereof. Particular examples of suitable
organic acids include, but are not limited to, caproic acid,
caprylic acid, capric acid, lauric acid, stearic acid, behenic
acid, erucic acid, oleic acid, linoleic acid, myristic acid,
benzoic acid, palmitic acid, phenylacetic acid, naphthalenoic acid,
dimerized derivatives thereof. The organic acids are aliphatic,
mono-functional (saturated, unsaturated, or multi-unsaturated)
organic acids. Salts of these organic acids may also be employed.
The salts of organic acids include the salts of barium, lithium,
sodium, zinc, bismuth, chromium, cobalt, copper, potassium,
strontium, titanium, tungsten, magnesium, cesium, iron, nickel,
silver, aluminum, tin, or calcium, salts of fatty acids,
particularly stearic, behenic, erucic, oleic, linoelic or dimerized
derivatives thereof. It is preferred that the organic acids and
salts of the present invention be relatively non-migratory (they do
not bloom to the surface of the polymer under ambient temperatures)
and non-volatile (they do not volatilize at temperatures required
for melt-blending.)
[0045] Other ingredients such as accelerators (for example, tetra
methylthiuram), processing aids, dyes and pigments, wetting agents,
surfactants, plasticizers, coloring agents, fluorescent agents,
chemical blowing and foaming agents, defoaming agents, stabilizers,
softening agents, impact modifiers, antioxidants, antiozonants, as
well as other additives known in the art may be added to the rubber
composition.
[0046] Other additives and fillers include, but are not limited to,
chemical blowing and foaming agents, optical brighteners, coloring
agents, fluorescent agents, whitening agents, UV absorbers, light
stabilizers, defoaming agents, processing aids, antioxidants,
stabilizers, softening agents, fragrance components, plasticizers,
impact modifiers, titanium dioxide pigment, acid copolymer wax,
surfactants, and fillers, such as zinc oxide, tin oxide, barium
sulfate, zinc sulfate, calcium oxide, calcium carbonate, zinc
carbonate, barium carbonate, tungsten, tungsten carbide, silica,
lead silicate, regrind (recycled material), clay, mica, talc,
nano-fillers, carbon black, glass flake, milled glass, and mixtures
thereof. Suitable additives are more fully described in, for
example, Rajagopalan et al., U.S. Patent Application Publication
No. 2003/0225197, the entire disclosure of which is hereby
incorporated herein by reference. In a particular embodiment, the
total amount of additive(s) and filler(s) present in the rubber
composition is 15 wt % or less, or 12 wt % or less, or 10 wt % or
less, or 9 wt % or less, or 6 wt % or less, or 5 wt % or less, or 4
wt % or less, or 3 wt % or less, based on the total weight of the
rubber composition. In a particular aspect of this embodiment, the
rubber composition includes filler(s) selected from carbon black,
nanoclays (e.g., Cloisite.RTM. and Nanofil.RTM. nanoclays,
commercially available from Southern Clay Products, Inc., and
Nanomax.RTM. and Nanomer.RTM. nanoclays, commercially available
from Nanocor, Inc.), talc (e.g., Luzenac HAR.RTM. high aspect ratio
talcs, commercially available from Luzenac America, Inc.), glass
(e.g., glass flake, milled glass, and microglass), mica and
mica-based pigments (e.g., Iriodin.RTM. pearl luster pigments,
commercially available from The Merck Group), and combinations
thereof. In a particular embodiment, the rubber composition is
modified with organic fiber micropulp, as disclosed, for example,
in Chen, U.S. Pat. No. 7,504,448, the entire disclosure of which is
hereby incorporated by reference.
[0047] Covers
[0048] The cores of the golf balls may be enclosed with one or more
cover layers so long as the outer cover layer is formed of the EPDM
rubber composition. The ball preferably includes a dual-cover
comprising inner and outer cover layers. The inner cover layer
preferably has a material hardness of 95 Shore C or less, or less
than 95 Shore C, or 92 Shore C or less, or 90 Shore C or less, or a
material hardness within a range having a lower limit of 60 or 65
or 70 or 75 or 80 or 84 or 85 Shore C and an upper limit of 90 or
92 or 95 Shore C. The thickness of the inner cover layer is
preferably within a range having a lower limit of 0.010 or 0.015 or
0.020 or 0.030 inches and an upper limit of 0.035 or 0.045 or 0.080
or 0.120 inches. The outer cover layer preferably has a material
hardness of 85 Shore C or less. The thickness of the outer cover
layer is preferably within a range having a lower limit of 0.010 or
0.015 or 0.025 inches and an upper limit of 0.035 or 0.040 or 0.055
or 0.080 inches. Preferably, the inner cover layer has a hardness
greater than the surface hardness of the outer cover layer.
[0049] A wide variety of materials may be used for forming the
inner cover including, for example, polyurethanes; polyureas;
copolymers, blends and hybrids of polyurethane and polyurea;
olefin-based copolymer ionomer resins (for example, Surlyn.RTM.
ionomer resins and DuPont HPF.RTM. 1000 and HPF.RTM. 2000,
commercially available from DuPont; Iotek.RTM. ionomers,
commercially available from ExxonMobil Chemical Company;
Amplify.RTM. IO ionomers of ethylene acrylic acid copolymers,
commercially available from The Dow Chemical Company; and
Clarix.RTM. ionomer resins, commercially available from A. Schulman
Inc.); polyethylene, including, for example, low density
polyethylene, linear low density polyethylene, and high density
polyethylene; polypropylene; rubber-toughened olefin polymers; acid
copolymers, for example, poly(meth)acrylic acid, which do not
become part of an ionomeric copolymer; plastomers; flexomers;
styrene/butadiene/styrene block copolymers;
styrene/ethylene-butylene/styrene block copolymers; dynamically
vulcanized elastomers; copolymers of ethylene and vinyl acetates;
copolymers of ethylene and methyl acrylates; polyvinyl chloride
resins; polyamides, poly(amide-ester) elastomers, and graft
copolymers of ionomer and polyamide including, for example,
Pebax.RTM. thermoplastic polyether block amides, commercially
available from Arkema Inc; cross-linked trans-polyisoprene and
blends thereof; polyester-based thermoplastic elastomers, such as
Hytrel.RTM., commercially available from DuPont; polyurethane-based
thermoplastic elastomers, such as Elastollan.RTM., commercially
available from BASF; synthetic or natural vulcanized rubber; and
combinations thereof.
[0050] The inner cover layer is preferably formed from a
composition comprising an ionomer or a blend of two or more
ionomers that helps impart hardness to the ball. Suitable ionomer
resins that may be used in the compositions of this invention are
generally referred to as copolymers of .alpha.-olefin; C.sub.3 to
C.sub.8 .alpha.,.beta.-ethylenically unsaturated mono- or
dicarboxylic acid; and optional softening monomer. The
.alpha.-olefin is preferably ethylene or C.sub.3 to C.sub.8. These
ionomers may be prepared by methods known in the art. Copolymers
may include, without limitation, ethylene acid copolymers, such as
ethylene/(meth)acrylic acid, ethylene/(meth)acrylic acid/maleic
anhydride, ethylene/(meth)acrylic acid/maleic acid mono-ester,
ethylene/maleic acid, ethylene/maleic acid mono-ester,
ethylene/(meth)acrylic acid/n-butyl(meth)acrylate,
ethylene/(meth)acrylic acid/iso-butyl(meth)acrylate,
ethylene/(meth)acrylic acid/methyl (meth)acrylate,
ethylene/(meth)acrylic acid/ethyl(meth)acrylate terpolymers, and
the like. The term "copolymer," as used herein, includes polymers
having two types of monomers, those having three types of monomers,
and those having more than three types of monomers. Preferred
.alpha.,.beta.-ethylenically unsaturated mono- or dicarboxylic
acids are (meth) acrylic acid, ethacrylic acid, maleic acid,
crotonic acid, fumaric acid, itaconic acid. (Meth) acrylic acid is
most preferred. As used herein, "(meth) acrylic acid" means
methacrylic acid and/or acrylic acid. Likewise, "(meth)acrylate"
means methacrylate and/or acrylate.
[0051] When a softening monomer is included, such copolymers are
referred to herein as E/X/Y-type copolymers, wherein E is ethylene;
X is a C.sub.3 to C.sub.8 .alpha.,.beta.-ethylenically unsaturated
mono- or dicarboxylic acid; and Y is a softening monomer. The
softening monomer is typically an alkyl (meth)acrylate, wherein the
alkyl groups have from 1 to 8 carbon atoms. Preferred E/X/Y-type
copolymers are those wherein X is (meth) acrylic acid and/or Y is
selected from (meth)acrylate, n-butyl(meth)acrylate,
isobutyl(meth)acrylate, methyl(meth)acrylate, and ethyl(meth)
acrylate. More preferred E/X/Y-type copolymers are ethylene/(meth)
acrylic acid/n-butyl acrylate, ethylene/(meth) acrylic acid/methyl
acrylate, and ethylene/(meth) acrylic acid/ethyl acrylate.
[0052] The amount of ethylene or C.sub.3 to C.sub.6 .alpha.-olefin
in the acid copolymer is typically at least 15 wt. %, preferably at
least 25 wt. %, more preferably least 40 wt. %, and even more
preferably at least 60 wt. %, based on the total weight of the
copolymer. The amount of C.sub.3 to C.sub.8
.alpha.,.beta.-ethylenically unsaturated mono- or dicarboxylic acid
in the acid copolymer is typically from 1 wt. % to 35 wt. %,
preferably from 5 wt. % to 30 wt. %, more preferably from 5 wt. %
to 25 wt. %, and even more preferably from 10 wt. % to 20 wt. %,
based on the total weight of the copolymer. The amount of optional
softening comonomer in the acid copolymer is typically from 0 wt. %
to 50 wt. %, preferably from 5 wt. % to 40 wt. %, more preferably
from 10 wt. % to 35 wt. %, and even more preferably from 20 wt. %
to 30 wt. %, based on the total weight of the copolymer. "Low acid"
and "high acid" ionomeric polymers, as well as blends of such
ionomers, may be used. In general, low acid ionomers are considered
to be those containing 16 wt. % or less of acid moieties, whereas
high acid ionomers are considered to be those containing greater
than 16 wt. % of acid moieties. In one version, the ionomer resin
preferably contains greater than 5 wt. % acid moieties and more
preferably greater than 11 wt. % acid moieties.
[0053] The acidic groups in the copolymeric ionomers are partially
or totally neutralized with a cation source. Suitable cation
sources include metal cations and salts thereof, organic amine
compounds, ammonium, and combinations thereof. Preferred cation
sources are metal cations and salts thereof, wherein the metal is
preferably lithium, sodium, potassium, magnesium, calcium, barium,
lead, tin, zinc, aluminum, manganese, nickel, chromium, copper, or
a combination thereof. The amount of cation used in the composition
is readily determined based on desired level of neutralization. For
example, ionomeric resins having acid groups that are neutralized
from about 10 percent to about 100 percent may be used. In one
embodiment, the acid groups are partially neutralized. That is, the
neutralization level is from about 10 to about 80%, more preferably
20 to 70%, and most preferably 30 to 50%. In another embodiment,
the acid groups are highly or fully neutralized. That is, the
neutralization level is from about 80 to about 100%, more
preferably 90 to 100%, and most preferably 95 to 100%.
[0054] It is also known that organic acids or salts of organic
acids, particularly fatty acids, may be added to the ionomer resin
to help make the composition more processable. This may be
accomplished by melt-blending an ethylene
.alpha.,.beta.-ethylenically unsaturated carboxylic acid copolymer,
for example, with an organic acid or a salt of organic acid, and
adding a sufficient amount of a cation source to increase the level
of neutralization of all the acid moieties (including those in the
acid copolymer and in the organic acid) to greater than 90%,
(preferably greater than 100%). The organic acids may be aliphatic,
mono- or multi-functional (saturated, unsaturated, or
multi-unsaturated) organic acids. Salts of these organic acids may
also be employed. The salts of organic acids of the present
invention include the salts of barium, lithium, sodium, zinc,
bismuth, chromium, cobalt, copper, potassium, strontium, titanium,
tungsten, magnesium, cesium, iron, nickel, silver, aluminum, tin,
or calcium, and salts of fatty acids, particularly stearic,
behenic, erucic, oleic, linoelic or dimerized derivatives thereof.
It is preferred that the organic acids and salts be relatively
non-migratory (they do not bloom to the surface of the polymer
under ambient temperatures) and non-volatile (they do not
volatilize at temperatures required for melt-blending).
[0055] In a particular embodiment, the inner cover layer is formed
from a composition comprising a high acid ionomer. A particularly
suitable high acid ionomer is Surlyn 8150.RTM. (DuPont). Surlyn
8150.RTM. is a copolymer of ethylene and methacrylic acid, having
an acid content of 19 wt %, which is 45% neutralized with sodium.
In another particular embodiment, the inner cover layer is formed
from a composition comprising a high acid ionomer and a maleic
anhydride-grafted non-ionomeric polymer. A particularly suitable
maleic anhydride-grafted polymer is Fusabond 525D.RTM. (DuPont).
Fusabond 525D.RTM. is a maleic anhydride-grafted,
metallocene-catalyzed ethylene-butene copolymer having about 0.9 wt
% maleic anhydride grafted onto the copolymer. A particularly
preferred blend of high acid ionomer and maleic anhydride-grafted
polymer is an 84 wt %/16 wt % blend of Surlyn 8150.RTM. and
Fusabond 525D.RTM.. Blends of high acid ionomers with maleic
anhydride-grafted polymers are further disclosed, for example, in
U.S. Pat. Nos. 6,992,135 and 6,677,401, the entire disclosures of
which are hereby incorporated herein by reference.
[0056] In one preferred embodiment, the inner cover layer is formed
from a composition comprising a 50/45/5 blend of Surlyn.RTM.
8940/Surlyn.RTM. 9650/Nucrel.RTM. 960, and, in a particularly
preferred embodiment, has a material hardness of from 80 to 85
Shore C. In another particular embodiment, the inner cover layer is
formed from a composition comprising a 50/25/25 blend of
Surlyn.RTM. 8940/Surlyn.RTM. 9650/Surlyn.RTM. 9910, preferably
having a material hardness of about 90 Shore C. In another version,
a blend of 50% Surlyn.RTM. 7940 and 50% Surlyn.RTM. 8940 is used to
form the inner cover. In yet another particular embodiment, the
inner cover layer is formed from a composition comprising a 50/50
blend of Surlyn.RTM. 8940/Surlyn.RTM. 8940/Surlyn 9650, preferably
having a material hardness of about 86 Shore C. Surlyn.RTM. 8940 is
an ethylene/methacrylic acid copolymer in which the MAA acid groups
have been partially neutralized with sodium ions. Surlyn.RTM. 9650
and Surlyn.RTM. 9910 are two different grades of
ethylene/methacrylic acid copolymer in which the MAA acid groups
have been partially neutralized with zinc ions. Surlyn.RTM. 7940 is
a copolymer of about 85% ethylene and 15% methacrylic acid that has
been neutralized with lithium ions. Nucrel.RTM. 960 is an
ethylene/methacrylic acid copolymer resin nominally made with 15 wt
% methacrylic acid, and available from DuPont.
[0057] As discussed above, the single or multi-layered core is
preferably enclosed with a dual-cover layer. In one embodiment, a
multi-layered cover comprising inner and outer cover layers is
formed, where the inner cover layer has a thickness of about 0.01
inches to about 0.06 inches, more preferably about 0.015 inches to
about 0.040 inches, and most preferably about 0.02 inches to about
0.035 inches. In this version, the inner cover layer is formed from
a partially- or fully-neutralized ionomer having a Shore D hardness
of greater than about 55, more preferably greater than about 60,
and most preferably greater than about 65. The outer cover layer,
in this embodiment, preferably has a thickness of about 0.015
inches to about 0.055 inches, more preferably about 0.02 inches to
about 0.04 inches, and most preferably about 0.025 inches to about
0.035 inches, with a hardness of about Shore D 70 or less, more
preferably 60 or less, and most preferably about 55 or less. The
inner cover layer is harder than the outer cover layer in this
version.
[0058] In another version, the outer cover is formed from a first
rubber composition comprising EPDM copolymer rubber, a
polymerization initiator, and a reactive cross-linking agent as
discussed above so that the outer cover has a hardness of 55 Shore
D or less. Meanwhile, the inner cover is formed from a second
rubber composition comprising EPDM copolymer rubber, a
polymerization initiator, and a reactive cross-linking agent so
that the inner cover has a hardness of 55 Shore D or greater. In
this embodiment, the same polymerization initiator and reactive
cross-linking agent used to form the inner cover layer can be used
to form the outer cover layer; provided, however, that the inner
cover layer has a hardness of 55 Shore D or greater and the outer
cover layer has a hardness of 55 Shore D or less.
[0059] Cores
[0060] The golf balls of this invention may contain single or
multi-layered cores. As discussed above, a polybutadiene rubber
composition is preferably used to form the core. Other suitable
thermosetting and thermoplastic materials can be used to form the
core if desired, such as, for example, polyurethanes, polyureas,
partially or fully neutralized ionomers, thermosetting polydiene
rubber such as polyisoprene or ethylene-propylene rubber or
ethylene-propylene-diene rubber natural rubber, balata, butyl
rubber, halobutyl rubber, styrene butadiene rubber or any styrenic
block copolymer such as styrene ethylene butadiene styrene rubber,
and the like, and metallocene or other single-site catalyzed
polyolefins, and combinations of two or more thereof. These other
thermosetting and thermoplastic materials can be used in place of
the polybutadiene rubber or can be mixed with the polybutadiene to
form a blend. In one preferred embodiment, the golf ball contains a
dual-core comprising an inner core (center) and surrounding outer
core layer. The inner core is preferably formed of a polybutadiene
rubber composition and surrounding outer core is preferably formed
of an EPDM rubber composition.
[0061] Preferably, the polybutadiene rubber-based inner core has a
center hardness (CH) within a range having a lower limit of 20 or
25 or 30 or 35 or 40 or 45 or 50 or 55 Shore C and an upper limit
of 60 or 65 or 70 or 75 or 80 or 85 or 90 or 95 Shore C. And,
preferably, the EPDM rubber-based outer core layer has a surface
hardness (OCLSH) within a range having a lower limit of 20 or 25 or
30 or 35 or 40 or 45 or 50 or 55 Shore C and an upper limit of 60
or 65 or 70 or 75 or 80 or 85 or 90 or 95 Shore C. Preferably, the
center hardness of the inner core layer is greater than the surface
hardness of the outer core layer. In one preferred embodiment, the
center hardness of the inner core is in the range of about 52 to
about 98 Shore C units and the surface hardness of the outer core
is in the range of about 50 to about 96 Shore C units. More
particularly, in one version, the center hardness of the inner core
is about 80 Shore C units or greater and the surface hardness of
the outer core is about 80 Shore C units or less. The center
hardness (inner core) is preferably at least 5 Shore C units
greater than the surface hardness (outer core).
[0062] The inner core preferably has a diameter within a range
having a lower limit of 0.40 or 0.75 or 0.85 or 0.875 inches and an
upper limit of 1.125 or 1.15 or 1.39 or 1.55 inches. The outer core
layer encloses the inner core such that the two-layered core has an
overall diameter within a range having a lower limit of 1.40 or
1.45 or 1.50 or 1.51 or 1.52 or 1.525 inches and an upper limit of
1.54 or 1.55 or 1.555 or 1.56 or 1.59 or 1.62 inches.
[0063] Golf Ball Constructions
[0064] As discussed above, the EPDM rubber compositions of this
invention may be used with any type of ball construction known in
the art. Such golf ball designs include, for example, three-piece,
four-piece, and five-piece designs.
[0065] The core and cover compositions may be prepared using
conventional mixing techniques. The core composition can be formed
into an inner core structure by ordinary techniques such as, for
example, injection or compression molding. After molding, the core
structure is removed from the mold and its surface may be treated
using techniques such as corona discharge, sand blasting, or
grinding to improve adhesion of the surrounding layers. Injection
molding or compression molding can be used to form an outer core
layer and/or inner cover layer about the inner core and produce an
intermediate golf ball. The outer cover layer is subsequently
molded over the inner cover layer to produce a golf ball.
[0066] In compression molding, the outer core and/or inner cover
composition is formed into smooth surfaced hemispherical shells
which are then positioned around the core in a mold having the
desired inner cover thickness and subjected to compression molding
under heat followed by cooling. This process fuses the shells
together to form a unitary intermediate ball. Alternatively, the
intermediate balls may be produced by injection molding, wherein
the outer core and/or inner cover layer is injected directly around
the core placed at the center of an intermediate ball mold under
heat and pressure. After molding, the golf balls produced may
undergo various further processing steps such as buffing, painting
and marking using conventional techniques to make a finished
ball.
[0067] Referring to FIG. 1, one version of a golf ball that can be
made in accordance with this invention is generally indicated at
(10). The ball (10) contains a core (12) surrounded by a dual-cover
(14) comprising inner and outer cover layers (14a, 14b). In FIG. 2,
a golf ball (16) containing a dual-core (18) with an inner core
(center) (18a) and outer core layer (18b) surrounded by a
dual-cover (20). having inner and outer cover layers (20a, 20b) is
shown. It also is recognized that golf balls containing other
multi-layered cores may be made in accordance with this
invention.
[0068] For example, in FIG. 3, a golf ball (24) containing an inner
core (center) (26), an intermediate core layer (28), and an outer
core layer (30) is shown. The cover comprises inner and outer cover
layers (32, 34). In this multi-layered core construction, the
center (26) preferably has a diameter within a range having a lower
limit of 0.100 or 0.125 or 0.250 inches and an upper limit of 0.375
or 0.400 or 0.500 or 0.750 or 1.00 inches. The intermediate core
layer (28) preferably has a thickness within a range having a lower
limit of 0.050 or 0.100 or 0.150 or 0.200 inches and an upper limit
of 0.300 or 0.350 or 0.400 or 0.500 inches. The outer core layer
(30) encloses the center (26) and intermediate core layer (28)
structure such that the multi-layer core has an overall diameter
within a range having a lower limit of 1.40 or 1.45 or 1.50 or 1.55
inches and an upper limit of 1.58 or 1.60 or 1.62 or 1.66
inches.
[0069] The center (26) preferably has an outer surface hardness of
70 Shore C or greater, more preferably a surface hardness of 80
Shore C or greater, and most preferably a surface hardness of 85
Shore C or greater. For example, the center (26) may have an outer
surface hardness within a range having a lower limit of 70 or 75 or
80 Shore C and an upper limit of 90 or 95 Shore C. The outer core
layer (30) preferably has an outer surface hardness that is less
than that of the center and is preferably 50 Shore C or less; or 60
Shore C or less; or 70 Shore C or less; or 75 Shore C or less; or
80 Shore C or less. The intermediate layer preferably has an inner
surface hardness greater than that of the center and outer core
layer hardness values. Preferably, the intermediate layer has a
surface hardness of 80 Shore C or greater.
[0070] In FIG. 4, a finished golf ball (10) having a cover
containing a dimpled pattern (36) is shown. Various dimple patterns
(36), as known in the art, may be used to modify the aerodynamic
properties of the ball.
[0071] It should be understood the golf balls shown in FIGS. 1-4
are for illustrative purposes only and not meant to be restrictive.
It should be recognized that other golf ball constructions can be
made in accordance with this invention.
[0072] Test Methods
[0073] Hardness. The center hardness of a core is obtained
according to the following procedure. The core is gently pressed
into a hemispherical holder having an internal diameter
approximately slightly smaller than the diameter of the core, such
that the core is held in place in the hemispherical portion of the
holder while concurrently leaving the geometric central plane of
the core exposed. The core is secured in the holder by friction,
such that it will not move during the cutting and grinding steps,
but the friction is not so excessive that distortion of the natural
shape of the core would result. The core is secured such that the
parting line of the core is roughly parallel to the top of the
holder. The diameter of the core is measured 90 degrees to this
orientation prior to securing. A measurement is also made from the
bottom of the holder to the top of the core to provide a reference
point for future calculations. A rough cut is made slightly above
the exposed geometric center of the core using a band saw or other
appropriate cutting tool, making sure that the core does not move
in the holder during this step. The remainder of the core, still in
the holder, is secured to the base plate of a surface grinding
machine. The exposed `rough` surface is ground to a smooth, flat
surface, revealing the geometric center of the core, which can be
verified by measuring the height from the bottom of the holder to
the exposed surface of the core, making sure that exactly half of
the original height of the core, as measured above, has been
removed to within 0.004 inches. Leaving the core in the holder, the
center of the core is found with a center square and carefully
marked and the hardness is measured at the center mark according to
ASTM D-2240. Additional hardness measurements at any distance from
the center of the core can then be made by drawing a line radially
outward from the center mark, and measuring the hardness at any
given distance along the line, typically in 2 mm increments from
the center. The hardness at a particular distance from the center
should be measured along at least two, preferably four, radial arms
located 180.degree. apart, or 90.degree. apart, respectively, and
then averaged. All hardness measurements performed on a plane
passing through the geometric center are performed while the core
is still in the holder and without having disturbed its
orientation, such that the test surface is constantly parallel to
the bottom of the holder, and thus also parallel to the properly
aligned foot of the durometer.
[0074] The outer surface hardness of a golf ball layer is measured
on the actual outer surface of the layer and is obtained from the
average of a number of measurements taken from opposing
hemispheres, taking care to avoid making measurements on the
parting line of the core or on surface defects, such as holes or
protrusions. Hardness measurements are made pursuant to ASTM D-2240
"Indentation Hardness of Rubber and Plastic by Means of a
Durometer." Because of the curved surface, care must be taken to
ensure that the golf ball or golf ball subassembly is centered
under the durometer indenter before a surface hardness reading is
obtained. A calibrated, digital durometer, capable of reading to
0.1 hardness units is used for the hardness measurements. The
digital durometer must be attached to, and its foot made parallel
to, the base of an automatic stand. The weight on the durometer and
attack rate conforms to ASTM D-2240.
[0075] In certain embodiments, a point or plurality of points
measured along the "positive" or "negative" gradients may be above
or below a line fit through the gradient and its outermost and
innermost hardness values. In an alternative preferred embodiment,
the hardest point along a particular steep "positive" or "negative"
gradient may be higher than the value at the innermost portion of
the inner core (the geometric center) or outer core layer (the
inner surface)--as long as the outermost point (i.e., the outer
surface of the inner core) is greater than (for "positive") or
lower than (for "negative") the innermost point (i.e., the
geometric center of the inner core or the inner surface of the
outer core layer), such that the "positive" and "negative"
gradients remain intact.
[0076] As discussed above, the direction of the hardness gradient
of a golf ball layer is defined by the difference in hardness
measurements taken at the outer and inner surfaces of a particular
layer. The center hardness of an inner core and hardness of the
outer surface of an inner core in a single-core ball or outer core
layer are readily determined according to the test procedures
provided above. The outer surface of the inner core layer (or other
optional intermediate core layers) in a dual-core ball are also
readily determined according to the procedures given herein for
measuring the outer surface hardness of a golf ball layer, if the
measurement is made prior to surrounding the layer with an
additional core layer. Once an additional core layer surrounds a
layer of interest, the hardness of the inner and outer surfaces of
any inner or intermediate layers can be difficult to determine.
Therefore, for purposes of the present invention, when the hardness
of the inner or outer surface of a core layer is needed after the
inner layer has been surrounded with another core layer, the test
procedure described above for measuring a point located 1 mm from
an interface is used.
[0077] Also, it should be understood that there is a fundamental
difference between "material hardness" and "hardness as measured
directly on a golf ball." For purposes of the present invention,
material hardness is measured according to ASTM D2240 and generally
involves measuring the hardness of a flat "slab" or "button" formed
of the material. Surface hardness as measured directly on a golf
ball (or other spherical surface) typically results in a different
hardness value. The difference in "surface hardness" and "material
hardness" values is due to several factors including, but not
limited to, ball construction (that is, core type, number of cores
and/or cover layers, and the like); ball (or sphere) diameter; and
the material composition of adjacent layers. It also should be
understood that the two measurement techniques are not linearly
related and, therefore, one hardness value cannot easily be
correlated to the other. Shore hardness (for example, Shore C or
Shore D hardness) was measured according to the test method ASTM
D-2240.
[0078] Compression. As disclosed in Jeff Dalton's Compression by
Any Other Name, Science and Golf IV, Proceedings of the World
Scientific Congress of Golf (Eric Thain ed., Routledge, 2002) ("J.
Dalton"), several different methods can be used to measure
compression, including Atti compression, Riehle compression,
load/deflection measurements at a variety of fixed loads and
offsets, and effective modulus. For purposes of the present
invention, "compression" refers to Atti compression and is measured
according to a known procedure, using an Atti compression test
device, wherein a piston is used to compress a ball against a
spring. The travel of the piston is fixed and the deflection of the
spring is measured. The measurement of the deflection of the spring
does not begin with its contact with the ball; rather, there is an
offset of approximately the first 1.25 mm (0.05 inches) of the
spring's deflection. Very low stiffness cores will not cause the
spring to deflect by more than 1.25 mm and therefore have a zero
compression measurement. The Atti compression tester is designed to
measure objects having a diameter of 42.7 mm (1.68 inches); thus,
smaller objects, such as golf ball cores, must be shimmed to a
total height of 42.7 mm to obtain an accurate reading. Conversion
from Atti compression to Riehle (cores), Riehle (balls), 100 kg
deflection, 130-10 kg deflection or effective modulus can be
carried out according to the formulas given in J. Dalton.
Compression may be measured as described in McNamara et al., U.S.
Pat. No. 7,777,871, the disclosure of which is hereby incorporated
by reference.
[0079] Coefficient of Restitution ("COR"). The COR is determined
according to a known procedure, wherein a golf ball or golf ball
subassembly (for example, a golf ball core) is fired from an air
cannon at two given velocities and a velocity of 125 ft/s is used
for the calculations. Ballistic light screens are located between
the air cannon and steel plate at a fixed distance to measure ball
velocity. As the ball travels toward the steel plate, it activates
each light screen and the ball's time period at each light screen
is measured. This provides an incoming transit time period which is
inversely proportional to the ball's incoming velocity. The ball
makes impact with the steel plate and rebounds so it passes again
through the light screens. As the rebounding ball activates each
light screen, the ball's time period at each screen is measured.
This provides an outgoing transit time period which is inversely
proportional to the ball's outgoing velocity. The COR is then
calculated as the ratio of the ball's outgoing transit time period
to the ball's incoming transit time period
(COR=V.sub.out/V.sub.in=T.sub.in/T.sub.out).
[0080] The present invention is further illustrated by the
following Examples, but these Examples should not be construed as
limiting the scope of the invention.
EXAMPLES
[0081] In the following Examples A-C, three-piece golf ball balls
were made. A polybutadiene-based solid core having a diameter of
about 1.55 inches was made using conventional techniques. Each core
was encapsulated with a Surlyn.RTM. ethylene-based acid copolymer
ionomer resin to form an inner cover. The ball subassembly (core
and inner cover) had a diameter of about 1.620 inches. Different
EPDM-based rubber outer cover formulations were prepared and these
formulations were molded over the subassemblies to form golf
balls.
TABLE-US-00001 Peroxide ZDA or Free- Zinc Base Secondary ZDMA
Radical Oxide Rubber Rubber Co-agent Initiator Filler Sample (phr)
(phr) (phr) (phr) (phr) A 80 Parts 20 parts 40 parts 4.5 parts 5
parts Nordel IP Buna 1220 ZDA Varox ZnO 5565 230XL B 80 parts 20
parts 30 parts 4.5 parts 5 parts Nordel IP Buna 1220 ZDA Varox ZnO
5565 230XL C 80 parts 20 parts 40 parts 4 parts 5 parts Nordel IP
Buna 1220 ZDMA Varox ZnO 5565 230XL Nordel .RTM. IP 5565-EPDM
rubber available from Dow Chemical Buna .RTM. 1220-polybutadiene
rubber available from Lanxess Corp. Varox .RTM. 230 XL-peroxide
granules available from R. T. Vanderbilt Co.
The resulting three-piece balls included an inner core, inner
cover, and an EPDM-based outer cover, and each of the balls showed
acceptable shear-durability.
[0082] When numerical lower limits and numerical upper limits are
set forth herein, it is contemplated that any combination of these
values may be used. Other than in the operating examples, or unless
otherwise expressly specified, all of the numerical ranges,
amounts, values and percentages such as those for amounts of
materials and others in the specification may be read as if
prefaced by the word "about" even though the term "about" may not
expressly appear with the value, amount or range. Accordingly,
unless indicated to the contrary, the numerical parameters set
forth in the specification and attached claims are approximations
that may vary depending upon the desired properties sought to be
obtained by the present invention.
[0083] All patents, publications, test procedures, and other
references cited herein, including priority documents, are fully
incorporated by reference to the extent such disclosure is not
inconsistent with this invention and for all jurisdictions in which
such incorporation is permitted.
[0084] It is understood that the compositions and golf ball
products described and illustrated herein represent only some
embodiments of the invention. It is appreciated by those skilled in
the art that various changes and additions can be made to
compositions and products without departing from the spirit and
scope of this invention. It is intended that all such embodiments
be covered by the appended claims.
* * * * *